This invention relates to electrically connecting printed circuit boards and other similar substrates in a vertical or z-axis direction to form a three-dimensional circuit module by using z-axis interconnectors, preferably of the type known as twist pins. More particularly, the present invention relates to a new and improved electrical connection in which one or more bulges of the interconnector establish electrical contact with and between the substrates without fully inserting the bulge into a plated through hole or via in at least one of the substrates, thereby simplifying the assembly, connection and disconnection of the substrates in the three-dimensional circuit module.
A variety of techniques have been developed for electrically connecting printed circuit boards, circuit components, substrates and/or other circuit elements into three-dimensional circuit modules. The propriety of using any one technique over another technique depends on the given situation and application for the module. Generally, the preferred technique in any situation is the one that enables the fastest, least-expensive and easiest assembly of the module in a manner which is consistent with the best use and longevity of the module. Additional considerations include the ease with which the module can be disassembled and reassembled, such as for troubleshooting or repair purposes.
To form a three-dimensional circuit module, usually a plurality of printed circuit boards, or substrates, are stacked vertically above one another. Vertical electrical connections between the stacked printed circuit boards are established by using z-axis interconnectors. Z-axis interconnectors extend vertically in the direction of the z-axis between the printed circuit boards which are oriented generally in a horizontal plane in the x-axis and y-axis directions. The z-axis interconnectors typically contact and extend through plated through holes or xe2x80x9cviasxe2x80x9d formed in each of the printed circuit boards. The electronic components and integrated circuits of each printed circuit board are connected to the vias by conductor traces formed on the surface of or within each printed circuit board. In this manner, the components of the printed circuit boards are connected to the components of one or more of the vertically stacked circuit boards, thereby creating a three-dimensional matrix of electrical connections, rather than limiting the electrical connections only to those elements on each circuit board. Consequently, a three-dimensional module of electrical connections and components is formed.
There are many benefits to three-dimensional circuit modules. One significant benefit is that a relatively large amount of electrical functionality can be obtained in a relatively small space or volume. This benefit maximizes the amount of electronic functionality for a given amount of space or reduces the amount of space required to obtain a given amount of electronic functionality.
To create the three-dimensional module, the vias are formed in each of the individual printed circuit boards at the same x-axis and y-axis locations, so that when the printed circuit boards are stacked in the three-dimensional module, the vias of the printed circuit boards are aligned vertically in the z-axis direction. The z-axis interconnectors are then inserted vertically through the aligned vias to establish the electrical contact and connection between the vertically separated circuit boards. Since the vias are connected to the electronic components on each circuit board by the traces, those components are also electrically interconnected in a three-dimensional manner.
A number of different types of z-axis interconnectors have been proposed. One particularly advantageous type of z-axis interconnector is known as a xe2x80x9ctwist pin.xe2x80x9d Twist pin z-axis interconnectors are described in U.S. Pat. Nos. 5,014,419, 5,064,192, and 5,112,232, all of which are assigned to the assignee hereof, as well as other prior art patents. General techniques for fabricating twist pins are described in these three patents, as well as in U.S. patent applications for a xe2x80x9cHigh-Speed, High-Capacity Twist Pin Connector Fabricating Machine and Method,xe2x80x9d Ser. No. 09/782,987; a xe2x80x9cWire Feed Mechanism and Method Used for Fabricating Electrical Connectors,xe2x80x9d Ser. No. 09/782,991; a xe2x80x9cRotational Grip Twist Machine and Method for Fabricating Bulges of Twisted Wire Electrical Connectors,xe2x80x9d Ser. No. 09/782,888; and a xe2x80x9cPneumatic Inductor and Method of Electrical Connector Delivery and Organization,xe2x80x9d Ser. No. 09/780,981, all of which are assigned to the assignee hereof. The use of z-axis interconnectors to create three-dimensional modules from printed circuit boards is described in U.S. Pat. No. 5,045,975, also assigned to the assignee hereof.
An example of a prior art twist pin 50 is shown in FIGS. 1 and 2. The twist pin 50 is formed from a length of wire 52 which has been formed conventionally by helically coiling a number of outer strands 54 around a center core strand 56 in a planetary manner. At selected, spaced-apart segments along the length of the wire 52, an expanded bulge 58 is formed by untwisting the outer strands 54 in a reverse or anti-helical direction. As a result of untwisting the strands 54 in the anti-helical direction, the space consumed by the outer strands 54 increases, causing the outer strands 54 to bend, expand and diverge outward from the center strand 56 at the axis of the twist pin. The outer strands 54 expand outward from the regularly twisted wire 52 in a pair of generally frustroconically-shaped expanding portions 57 which meet at a maximum-diameter or maximum-width portion 59. At the maximum-width portion 59, the diameter for the bulge 58 is larger than the diameter of the regular stranded wire 52. The laterally outward extent of the maximum-width portion 59 of the bulge 58 is exemplified in FIG. 3, compared to FIG. 2.
The twist pin 50 has mechanical characteristics to maintain the shape of the wire in the expanded configuration, to allow the outer strands 54 to diverge outward in the expanding portions 57 to the maximum-width portion 59 at each bulge 58 when untwisted, and to cause the strands 54 at the maximum-width portion 59 to compress radially inward toward the center strand 56 when the bulge is inserted into a via of the printed circuit board. The radial compression of the outer strands 54 toward the center strand 56 at the bulge applies resilient radial contact force against a side wall of a via to establish the electrical connection of the twist pin to the via of the printed circuit board and to resist longitudinal movement of the twist pin relative to the printed circuit board.
The bulges 58 are positioned at selected predetermined distances along the length of the wire 52 to contact the vias 60 in printed circuit boards 62 of a three-dimensional module 64, as shown in FIG. 4. Contact of the bulges 58 with the vias 60 is established by pulling the twist pin 50 through an aligned vertical column of vias 60 in the module 64 while the printed circuit boards 62 are held in position. The resiliency of the outer strands 54 of the wire 52 at the bulges 58, when compressed radially inward by insertion into the somewhat smaller via 58, press against an inner surface of a sidewall 66 of each via 60, and thereby establish the electrical connection between the twist pin 50 and the via 60, as shown in FIG. 5.
To insert the twist pins 50 into the vertically aligned vias 60 of the module 64 with the bulges 58 contacting the inner surfaces 66 of the vias 60, a leader 68 of the regularly-coiled strands 54 and 56 extends at one end of the twist pin 50. The strands 54 and 56 at a terminal end 70 of the leader 68 have been welded or fused together to form a rounded end configuration 70 to facilitate insertion of the twist pin 50 through the column of vertically aligned vias. The leader 68 is of sufficient length to extend through all of the vertically aligned vias 60 of the assembled stacked printed circuit boards 62, before the first bulge 58 makes contact with the outermost via 60 of the outermost printed circuit board 62. The end of the leader 68 is gripped on the outside of the stacked printed circuit boards, and the twist pin 50 is pulled through the vertically aligned vias 60 until the bulges 58 are aligned and in contact with the vias 60 of the stacked printed circuit boards. To position the bulges in contact with the vertically aligned vias, the leading bulges 58 will be pulled into and out of most of the vertically aligned vias until the twist pin 50 arrives at its final desired position. The resiliency of the strands 54 allow the bulges 58 to move in and out of the vias without losing their ability to make sound electrical contact with the sidewall of the final desired via 60 into which the bulges 58 are positioned.
Once appropriately positioned, the leader 68 is cut off so that the end of the twist pin 50 is approximately at the same level or slightly beyond the outer surface of the outer printed circuit board of the module 64. The cut off leader 68 is then discarded. A tail 72 at the other end of the twist pin 50 extends a shorter distance beyond the last bulge 58. The strands 54 and 56 at a terminal end 74 of the tail 72 are also fused together. The length of the tail 72 positions the end 74 at a similar position to the location where the leader 68 was cut on the opposite side of the module. However, if desired, the length of the tail 72 or the remaining length of the leader 68 after it is cut may be made longer or shorter.
One of the difficulties of assembling the three-dimensional circuit module using twist pins in this manner is that it is necessary to retain the printed circuit boards at precise vertical intervals, so that the bulges of the twist pin contact and fit within the vias. Retaining the printed circuit boards at the vertical intervals can be tedious, particularly when the printed circuit boards are relatively small and when no mechanical spacers other than the twist pins hold the printed circuit boards together in the three-dimensional module. Moreover, pulling the leading bulges through many of the aligned vias before reaching the final desired position offers the possibility of damaging the plated through vias, or possibly damaging the circuit boards, by the force created in pulling the bulges through the vias.
It is sometimes necessary to disassemble the printed circuit boards from the three-dimensional module to repair or replace any defective components. Allowing the tail 72 and the remaining portion of the leader 68 to extend slightly beyond the outer printed circuit boards 62 of the module 64 facilitates gripping the twist pin 50 to pull it out of the module. Once the leader 68 is cut off after initial assembly, the twist pin 50 cannot be reused, because there is no leader available to pull it through the aligned vias. Upon reassembly, then, all of the above described steps must be repeated using a new twist pin.
The use of the z-axis interconnectors or twist pins as described herein enables fast, efficient, reliable assembly, as well as disassembly and reassembly, of a plurality of substrates, such as printed circuit boards, in a three-dimensional module. A first bulge of a twist pin is fully inserted into a via to hold the twist pin relative to the circuit board as result of the conventional compressive force of the bulge against the side wall of the via. However, a second longitudinally-spaced bulge of the twist pin is not fully inserted into a via. Instead, the expanding portion of the second bulge contacts an edge of the via without the maximum-width portion of the bulge moving completely into compressive contact with the side wall of the via. An electrical connection is established by radial compression of the expanding portion of the second bulge against the edge of the via. The adequacy of the connection is caused by the contact of the expanding portion of the bulge with a corner edge of the via, or by such contact and the effect of the fully inserted first bulge. The compression force of the fully inserted first bulge in the via resists movement of the twist pin in a direction which would relieve the contact force from the expanding portion of the second bulge with the corner edge of the via thereby maintaining the electrical contact in one aspect of the invention.
In another aspect of the invention, the contact of the expanding portion of the bulge creates sufficient force to establish electrical contact of a terminal end of the twist pin with a flat contact surface of an adjoining substrate or circuit board in the module. In a further aspect of the invention, the opposite expanding portions of a single bulge contact the corner edges of two vias in two spaced apart printed circuit boards or substrates, thereby establishing the electrical connection through the single bulge.
Because electrical contact is established without requiring the bulge to be fully inserted in the via, the assembly of the three-dimensional module is facilitated because the bulges do not have to be pulled through all of the aligned vias. Instead, the twist pin is connected to one circuit board, preferably by inserting the twist pin until the first fully-inserted bulge is located in the desired location, and then the adjoining second circuit board is retained relative to the first circuit board. The electrical contact to the second circuit board is established by contacting the expanding portion of the non-fully inserted second bulge with the corner edge. Not only is assembly facilitated in this manner, but for alignment purposes, the fully inserted and fully radially compressed first bulge will permit the entire twist pin to move longitudinally a sufficient amount to self-adjust or self-align itself with adequate contact force from the expanding portion of the non-inserted second bulge to establish a good electrical connection. Thus, the force created by the contact of the expanding portion of the bulge with the corner edge of the via may also be sufficient to reposition the first, fully inserted and radially compressed bulge within its via so that the second non-inserted bulge nevertheless makes sufficient contact to establish a good electrical connection, or to reposition the terminal end of the twist pin in good electrical connection with the flat contact connection surface of the adjoining substrate, or to establish good contact of the single bulge with the corner edge of two vias.
During assembly, the expanding portion of the bulge is biased against the corner edge while the substrates are held together. However, the twist pin is not retained by both substrates, but is only pressed against one of them. In this manner, upon disassembly or disconnection of the substrates, the twist pin loses contact with the one substrate without being pulled or pushed out of the other substrate. The substrates may then be reassembled without having to remove or replace the twist pin. Moreover, a new twist pin need not be used for reassembly.
Although described above in terms of a twist pin, the broader aspects of the invention apply to z-axis interconnectors or pins having bulges. The broader aspects of the invention also apply to connecting all types of substrates upon which electronic components are formed or connected or supported, including printed circuit boards and substrates made from composites, ceramics and other types of materials suitable for electronic circuit use. A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above noted and other improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims.